As is known, some fluids are processed at temperatures that should be regulated in an increasingly more accurate way, in particular when chemical or biochemical reactions are involved. In addition to this requirement, there is often also the need to use very small quantities of fluid, owing to the cost of the fluid, or to low availability.
This is the case, for example, of the DNA amplification process (PCR, i.e., Polymerase Chain Reaction process), wherein accurate temperature control in the various steps (repeated pre-determined thermal cycles are carried out), the need to avoid as far as possible thermal gradients where fluids react (to obtain here a uniform temperature), and also reduction of the used fluid (which is very costly), are of crucial importance in obtaining good reaction efficiency, or even to make reaction successful.
Other examples of fluid processing with the above-described characteristics are associated for example with implementation of chemical and/or pharmacological analyses, and biological examinations, etc.
At present, various techniques allow thermal control of chemical or biochemical reagents. In particular, from the end of the '80s, miniaturized devices were developed, and thus had a reduced thermal mass, which could reduce the times necessary to complete the DNA amplification process. Recently, monolithic integrated devices of semiconductor material have been proposed, able to process small fluid quantities with a controlled reaction, and at a low cost (see, for example, U.S. patent applications Ser. No. 09/779,980 filed on Feb. 8, 2001, and 09/874,382 filed on Jun. 4, 2001, assigned to STMicroelectronics, S.r.1.).
These devices comprise a semiconductor material body accommodating buried channels that are connected, via an input trench and an output trench, to an input reservoir and an output reservoir, respectively, to which the fluid to be processed is supplied, and from which the fluid is collected at the end of the reaction. Above the buried channels, heating elements and thermal sensors are provided to control the thermal conditions of the reaction (which generally requires different temperature cycles, with accurate control of the latter), and, in the output reservoir, detection electrodes are provided for examining the reacted fluid.
In chemical microreactors of the described type, the problem exists of thermally insulating the reaction area (where the buried channels and the heating elements are present) from the detection area (where the detection electrodes are present). In fact, the chemical reaction takes place at high temperature (each thermal cycle involves a temperature of up to 94° C.), whereas the detection electrodes must be kept at a constant ambient temperature.